The direct lens test pages for the pancakes are as follows:-
SMC DA 15mm F4 ED AL Limited
SMC DA 21mm F3.2 AL Limited
SMC DA 40mm F2.8 Limited
SMC DA 70mm F2.4 Limited
Well, the results of those wider lenses are not that good. I have the DA21 and 70 pancakes and would agree that resolution wise the DA21 is really not "sharp" enough but it is not that worst neither, IMHO.
Note also that the T-stop measurement and scoring (which affects the overall test score) is not completely fair to all those Pentax Limited primes, which are known to be slow actually, for what they were meant to, i.e., for the compact and lightweight design.